Adriano J. G. Otuka

Emission features of microstructures fabricated by two-photon polymerization containing three organic dyes

Fabrication of microstructures containing active compounds, such as fluorescent dyes and nanoparticles have been exploited in the last few years, aiming at applications from photonics to biology. Here we fabricate, using two-photon polymerization, microstructures containing the fluorescent dyes Stilbene 420, Disodium Fluorescein and Rhodamine B. The produced microstructures, containing dyes at specific sites, present good structural integrity and a broad fluorescence spectrum, from about 350 nm until 700 nm. Such spectrum can be tuned by using different excitation wavelengths and selecting the excitation position in the microstructure. These results are interesting for designing multi-doped structures, presenting tunable and broad fluorescence spectrum.

Direct laser writing by two-photon polymerization as a tool for developing microenvironments for evaluation of bacterial growth

Monitoring bacteria growth and motion in environments is fundamental to understand, for instance, how they proliferate and contaminate organism. Therefore, techniques to fabricate microenvironments for in situ and in vivo studies are interesting for that purpose. In this work we used two-photon polymerization to fabricate microenvironments and, as a proof of principle, we demonstrated the development of the bacteria ATCC 25922 Escherichia coli (E. coli) into the microstructure surroundings. Two varieties of polymeric microenvironments are presented: (i) a microenvironment doped at specific site with ciprofloxacin, an antibiotic typically used in the treatment of diseases caused by E. coli and (ii) micro-fences, which serve as traps for bacteria. These microenvironments, fabricated by two-photon polymerization, may be a potential platform for drug delivery system, by promoting or inhibiting the growth of bacteria in specific biological or synthetic sites.

Two-Photon Polymerization Fabrication of Doped Microstructures

Scientists and engineers have sought to design more compact and efficient devices by means of microfabrication techniques. Examples of microfabrication processes include lithography, chemical vapor deposition, sol-gel, dry etching, among others. Although every technique has its own specificities and advantages, most of them are multi-step processes and demand long time of fabrication. Because of such limitations, and also because of the small range of materials that can be used in these techniques, there has been extensive search for alternative microdevice fabrication methods. A new microfabrication technique, called two-photon polymerization (2PP), emerged in 1997 opening a wider range of material possibilities with the advantage of allowing tridimensional fabrication. In this technique, Maruo et al (Maruo, et al., 1997) employed a laser-based-apparatus to fabricate three-dimensional polymeric microstructures with no topological constrains, high penetration depth without surface modifications and resolution bellow the diffraction limit. This technique usually employs femtosecond laser pulses to promote two-photon absorption (2PA) of a photosensitive molecule dissolved into the bulk of an unpolymerized resin, which creates a radical and triggers polymerization in a confined spatial region.

Femtosecond lasers for processing glassy and polymeric materials

Novel materials have been developed to meet the increasing mechanical, electrical and optical properties required for technological applications in different fields of sciences. Among the methods available for modifying and improving materials properties, femtosecond laser processing is a potential approach. Owing to its precise ablation and modification capability, femtosecond laser processing has already been employed in a broad range of materials, including glasses and polymers. When ultrashort laser pulses are focused into a transparent material, the intensity at the focus can become high enough to induce nonlinear optical processes. Here, we report on femtosecond (fs) laser microfabrication in special glasses and polymers. Initially, we describe fs-laser micromachining on the surface of copper doped borate and borosilicate glasses. Subsequently, we present results on two-photon induced polymerization to fabricate microstructures containing fluorescent dyes for manufacturing optical microcavities. Both approaches are promising for designing optical and photonics micro/nanodevices.

Laser induced periodic surface structuring on Si by temporal shaped femtosecond pulses.

We investigated the effect of temporal shaped femtosecond pulses on silicon laser micromachining. By using sinusoidal spectral phases, pulse trains composed of sub-pulses with distinct temporal separations were generated and applied to the silicon surface to produce Laser Induced Periodic Surface Structures (LIPSS). The LIPSS obtained with different sub-pulse separation were analyzed by comparing the intensity of the two-dimensional fast Fourier Transform (2D-FFT) of the AFM images of the ripples (LIPSS). It was observed that LIPSS amplitude is more emphasized for the pulse train with sub-pulses separation of 128 fs, even when compared with the Fourier transform limited pulse. By estimating the carrier density achieved at the end of each pulse train, we have been able to interpret our results with the Sipe-Drude model, that predicts that LIPSS efficacy is higher for a specific induced carrier density. Hence, our results indicate that temporal shaping of the excitation pulse, performed by spectral phase modulation, can be explored in fs-laser microstructuring.

Optical microdevices fabricated using femtosecond laser processing (Conference Presentation)

Femtosecond laser processing techniques have been widely employed to produce micro or nanodevices with special features. These devices can be selectively doped with organic dyes, biological agents, nanoparticles or carbon nanotubes, increasing the range of applications. Acrylate polymers can be easily doped with various compounds, and therefore, they are interesting materials for laser fabrication techniques. In this work, we use multiphoton absorption polymerization (MAP) and laser ablation to fabricate polymeric microdevices for optical applications. The polymeric sample used in this work is composed in equal proportions of two three-acrylate monomers; while tris(2-hydroxyethyl)isocyanurate triacrylate gives hardness to the structure, the ethoxylated(6) trimethyl-lolpropane triacrylate reduces the shrinkage tensions upon polymerization. These monomers are mixed with a photoinitiator, the 2,4,6-trimetilbenzoiletoxifenil phosphine oxide, enabling the sample polymerization after laser irradiation. Using MAP, we fabricate three-dimensional structures doped with fluorescent dyes. These structures can be used in several optical applications, such as, RGB fluorescent microdevices or microresonators. Using azo compounds like dopant in the host resin, we can apply these structures in optical data storage devices. Using laser ablation technique, we can fabricate periodic microstructures inside polymeric bulks doped with xanthene dyes and single-walled carbon nanotubes, aiming applications in random laser experiments. In structured bulks we observed multi-narrow emission peaks over the xanthene fluorescence emission. Furthermore, in comparison with non-structured bulks, we observed that the periodic structure decreased the degree of randomness, reducing the number of peaks, but defining their position.

Fabrication of waveguides in doped organic/Silica hybrid materials using femtosecond laser pulses

Fabrication of waveguides using femtosecond laser micromachining technique in Rhodamine B-doped organic/Silica hybrid materials is demonstrated. Optical properties and microscopic images were measured; and the produced waveguides present 2.3 dB/mm total loss.

Two-photon Polymerization Microfabrication of Double Doped Structures

The doping of the microstructures allows the fabrication of devices with specific features. In this work, we developed a method for fabricating microstructures, by two-photon absorption polymerization, that can be doped with different dopants.